This is a note to let you know that I've just added the patch titled sched,psi: Handle potential task count underflow bugs more gracefully to the 5.11-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: sched-psi-handle-potential-task-count-underflow-bugs.patch and it can be found in the queue-5.11 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 02c56f07688107514908411300857b161d352d33 Author: Charan Teja Reddy <charante@xxxxxxxxxxxxxx> Date: Fri Apr 16 20:32:16 2021 +0530 sched,psi: Handle potential task count underflow bugs more gracefully [ Upstream commit 9d10a13d1e4c349b76f1c675a874a7f981d6d3b4 ] psi_group_cpu->tasks, represented by the unsigned int, stores the number of tasks that could be stalled on a psi resource(io/mem/cpu). Decrementing these counters at zero leads to wrapping which further leads to the psi_group_cpu->state_mask is being set with the respective pressure state. This could result into the unnecessary time sampling for the pressure state thus cause the spurious psi events. This can further lead to wrong actions being taken at the user land based on these psi events. Though psi_bug is set under these conditions but that just for debug purpose. Fix it by decrementing the ->tasks count only when it is non-zero. Signed-off-by: Charan Teja Reddy <charante@xxxxxxxxxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx> Link: https://lkml.kernel.org/r/1618585336-37219-1-git-send-email-charante@xxxxxxxxxxxxxx Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c index 967732c0766c..651218ded981 100644 --- a/kernel/sched/psi.c +++ b/kernel/sched/psi.c @@ -711,14 +711,15 @@ static void psi_group_change(struct psi_group *group, int cpu, for (t = 0, m = clear; m; m &= ~(1 << t), t++) { if (!(m & (1 << t))) continue; - if (groupc->tasks[t] == 0 && !psi_bug) { + if (groupc->tasks[t]) { + groupc->tasks[t]--; + } else if (!psi_bug) { printk_deferred(KERN_ERR "psi: task underflow! cpu=%d t=%d tasks=[%u %u %u %u] clear=%x set=%x\n", cpu, t, groupc->tasks[0], groupc->tasks[1], groupc->tasks[2], groupc->tasks[3], clear, set); psi_bug = 1; } - groupc->tasks[t]--; } for (t = 0; set; set &= ~(1 << t), t++)